• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.35-47
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• 2003

Seismic ground motion can vary significantly over distances comparable to the length of a majority of highway bridges on multiple supports. This paper presents results of fragility analysis of two actual highway bridges under ground motion with spatial variation. Ground motion time histories are artificially generated with different amplitudes, phases, as well as frequency contents at different support locations. Monte Carlo simulation is performed to study dynamic responses of the bridges under these ground motions. The effect of spatial variation on the seismic response is systematically examined and the resulting fragility curves are compared with those under identical support ground motion. This study shows that ductility demands for the bridge columns can be underestimated if the bridge is analyzed using identical support ground motions rather than differential support ground motions. Fragility curves are developed as functions of different measures of ground motion intensity including peak ground acceleration(PGA), peak ground velocity(PGV), spectral acceleration(SA), spectral velocity(SV) and spectral intensity(SI). This study represents a first attempt to develop fragility curves under spatially varying ground motion and provides information useful for improvement of the current seismic design codes so as to account for the effects of spatial variation in the seismic design of long-span bridges.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.8
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• pp.808-812
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• 2008

In recent years, the software vulnerability becomes an important problem to the safety in operating system kernel. Many organizations endeavor to publish patches soon after discovery of vulnerability. In spite of the effort, end-system administrators hesitate to apply the patches to their system. The reasons of hesitation are the reboot disruption and the distrust of patches. To solve this problem we propose a dynamic update system for non-updatable kernel, named DUNK. The DUNK provides: 1) a dynamic update mechanism at function-level granularity to overcome the reboot disruption and 2) a safety verification mechanism to overcome the distrust problem, named MAFIA. In this paper, we describe the design of DUNK and detailed algorithm of MAFIA.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.6
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• pp.412-421
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• 2013

Nowadays, small and medium-sized earthquakes occur frequently in the west coast of Korea. The earthquake induced damages on the harbor structure such as quay wall possibly make a severe impact on national economy. Therefore, not only a seismic design for the structures but warning system for seismic damage right after the occurrence of earthquake should be developed. In this study, seismic fragility analysis was performed to be given to earthquake damage prediction system for quay wall structures in Busan and Incheon harbor. Four types of structures such as pier-type, caisson type, counterfort type, block-type were analyzed and fragility curves of functional performance level and collapse prevention level based on displacement criteria were found. Regression analyses by using the results of the two ports were done for possible use in other port structures.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.193-193
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• 2023

여러 기후변화 시나리오에 의하면 기상재해의 발생빈도 및 강도가 증가할 것으로 예상된다. 그중 가뭄은 강수량 부족, 하천유량 감소, 토양 함수량 감소, 용수 수요량 증가 등의 다양한 요인으로 인해 발생하며, 한 가지 형태뿐만 아니라 복합적인 형태로 발생할 수 있다. 또한, 우리나라는 지역마다 기후 특성의 편차가 있어 기후변화에 따른 가뭄 취약성과 대응 능력이 지역마다 다르게 나타난다. 따라서 가뭄에 대응하기 위해서는 다양한 요인을 고려한 통합가뭄지수를 활용해야 하며, 미래의 기후변화를 고려하여 종합적으로 가뭄을 평가해야 한다. 본 연구에서는 동적 베이지안 분류기(DNBC) 기반의 통합가뭄지수를 활용하여 우리나라 전국에 대해 수문학적 위험도를 분석하고 미래 가뭄을 전망하였다. 기상학적, 수문학적, 농업적 및 사회경제적 요인을 고려한 통합가뭄지수를 산정하기 위하여 DNBC 분류기의 인자로 기후변화 시나리오 기반의 기상학적 가뭄지수 SPI, 수문학적 가뭄지수 SDI, 농업적 가뭄지수 ESI와 사회경제적 가뭄지수 WSCI를 활용하였다. 산정된 통합가뭄지수의 시계열을 기반으로 심도와 지속기간을 추출하고, 코플라 함수를 활용한 이변량 가뭄빈도분석을 수행하였다. 이후, 이변량 가뭄빈도분석에 의해 산정된 재현기간을 활용하여 수문학적 위험도를 산정하였다. 그 결과, P1(2021~2040) 기간이 수문학적 위험도 R=0.588로 가장 높은 위험도를 나타냈으며, 이후 P2(2041~2070) 기간까지 감소하였다가 P3(2071~2099) 기간에 다시 증가하는 추세를 보였다. P1(2021~2040) 기간과 P3(2071~2099) 기간은 영산강 유역이 각각 R=0.625(P1), R=0.550(P3)으로 가장 높은 위험도를 나타냈으나, P2(2041~2070) 기간은 금강 유역이 수문학적 위험도 R=0.482로 가장 높게 나타났다. 본 연구결과를 통해 향후 미래 가뭄에 대한 가뭄계획 수립 시에 기초자료로서 활용성이 높을 것으로 기대된다.

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.99-108
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• 2009

Since the preexisting evaluation methods of landslide susceptibility take somehow long time to determine the slope stability based on the field survey and laboratory analysis, there are several problems to acquire immediate evaluation results in the field. In order to overcome the previously mentioned problems and incorrect evaluation results induced by some subjective evaluation criteria and methods, this study tried to develop a method of landslide susceptibility by a quantitative and objective evaluation approach based on the field survey. Therefore, this study developed an evaluation chart for landslide susceptibility on natural terrain using the AHP analysis method to predict landslide hazards on the field sites. The AHP analysis was performed by a questionnaire to several specialists who understands mechanism and influential factors of landslide. Based on the questionnaire, weighting values of criteria and alternatives to influence landslide triggering were determined by the AHP analysis. According to the scoring results of the analysed weighting values, slope angle is the most significant factor. Permeability, water contents, porosity, lithology, and elevation have the significance to the landslide susceptibility in a descending order. Based on the assigned scores of each criterion and alternatives of the criteria, an evaluation chart for landslide susceptibility was suggested. The evaluation chart makes it possible for a geologist to evaluate landslide susceptibility with a total score summed up each alternative score.

• Journal of Korea Water Resources Association
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• v.49 no.3
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• pp.217-225
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• 2016

The drought is generally characterized by duration and severity, thus it is required to conduct the bivariate frequency analysis simultaneously considering the drought duration and severity. However, since a bivariate joint probability distribution function (JPDF) has a 3-dimensional space, it is difficult to interpret the results in practice. In order to suggest the technical solution, this study employed copula functions to estimate an JPDF, then developed conditional JPDFs on various drought durations and estimated the critical severity corresponding to non-exceedance probability. Based on the historical severe drought events, the hydrologic risks were investigated for various extreme droughts with 95% non-exceedance probability. For the drought events with 10-month duration, the most hazardous areas were decided to Gwangju, Inje, and Uljin, which have 1.3-2.0 times higher drought occurrence probabilities compared with the national average. In addition, it was observed that southern regions were much higher drought prone areas than northern and central areas.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.21-21
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• 2023

현재 구축되어있는 방재시설의 능력은 기후위기로 인해 수용가능한 극한강우량의 범위를 넘어서고 있어 대형화된 홍수로 인한 피해가 꾸준히 발생하고 있다. 이로 인해 잠재적 홍수로 인한 도시회복도 관리와 홍수로 수반되는 피해에 대한 복구의 중요도가 높아지고 있다. 회복도는 도시의 재해 취약성, 저항, 적응, 복구, 완화에 대한 능력을 포괄하는 개념으로써 최근 주목받고 있는 개념이지만 대부분의 연구는 주로 시설에 대한 회복도 평가가 이루어지고 있다 (Sen et al.,2021). 또한 재해 후 도시복구에 관한 연구는 다수 존재하지만 복구에 따른 지역의 회복도 변화와 라이프라인과 같은 주요 시설의 복구에 따른 회복도 차이를 고려한 연구는 미비한 실정이다. 따라서 본 연구에서는 도시침수 발생 후 라이프라인을 고려한 도시복구 우선순위 산정모델을 개발하고 재해관리의 효율성 향상측면에서 도시의 기능적 회복도를 평가하였다. 이를 위해 라이프라인 중 도로 복구결과의 평가를 위하여 리스크 매트릭스 기법을 이용한 도로위험도평가를 수행하였으며 도시의 회복도를 측정하였다. 회복도를 크게 홍수로부터 도시가 받은 영향과 재해복구역량으로 구성하였으며 정량적인 평가를 위해 각각 손상함수와 재해재난목적예비비를 활용하여 산정하였다. 이후 복구우선순위를 산정하였으며 복구와 도시회복도와의 관계를 분석하기 위하여 재해연보 자료를 기초로 회귀분석을 통해 복구비용을 추정하였다 (유순영 등.,2014). 시범지역에 적용한 결과 시설 및 도로 복구에 따른 도시영향의 변화보다 복구비사용으로 인한 재해복구역량의 변화가 더욱 크다는 것을 확인하였다. 이는 재해재난목적예비비의 중요성이 크다는 것을 의미하며 향후 추가적인 인문학적, 법제적 요소가 회복도에 미치는 영향을 연구한다면 도시회복도 향상 및 도시복구에 관한 정책적 의사결정에 큰 도움이 될 것이다.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.443-447
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• 2011

최근 수재해는 중소하천을 부근에서 주로 발생하고 있는 것이 사실이며 중소하천에서 수재해 발생 여부를 선재적으로 파악하여 비상시 피해를 최소화할 수 있는 적절한 수위관측망의 설치가 필요하다. 따라서 본 연구에서는 중소하천에서 최적 수위관측망을 구성하기 위한 방법론으로 각 소유역의 단위도를 유도하여 확률밀도함수를 이용한 후 엔트로피 이론을 적용하였다. 또한 재해에 취약한 재해위험지구를 분류하여 수위관측소의 설치가 필요하다고 판단되는 지점을 우선적으로 선택할 수 있도록 방법론을 설정하여 낙동강 유역의 중소유역을 대상으로 적용하였다. 적용 결과 각 중소하천에서의 소수의 수위관측소들이 비선정된 것을 제외하고 대다수가 선정되었다. 이와 같은 방법론은 방재측면을 고려한 수위관측망을 구성하기 위하여 유용하게 활용될 수 있을 것으로 기대된다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.22 no.5
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• pp.1159-1168
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• 2012

Control Flow Integrity(CFI) and Control Flow Locking(CFL) prevent unintended execution of software and provide integrity in control flow. Attackers, however, can still hijack program controls since CFI and CFL does not support fine-granularity, context-sensitive protection. In this paper, we propose a new CFI scheme, Source-code CFI(SCFI), to overcome the problems. SCFI provides context-sensitive locking for control flow. Thus, the proposed approach protects software against the attacks on the previous CFI and CFL schemes and improves safety.

• Journal of the Korean Geotechnical Society
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• v.35 no.11
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• pp.111-119
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• 2019

The high-speed railway system is mainly composed of tunnel, bridge, and viaduct to meet the straightness needed for keeping the high speed up to 400 km/s. Seismic fragility for the high-speed railway infrastructure can be assessed as two ways: one way is studying each element of infrastructure analytically or numerically, but it requires lots of research efforts due to wide range of railway system. On the other hand, empirical method can be used to access the fragility of an entire system efficiently, which requires case history data. In this study, we collect the 2004 M_W 6.6 Niigata earthquake case history data to develop empirical seismic fragility function for a railway system. Five types of intensity measures (IMs) and damage levels are assigned to all segments of target system for which the unit length is 200 m. From statistical analysis, probability of exceedance for a certain damage level (DL) is calculated as a function of IM. For those probability data points, log-normal CDF is fitted using MLE method, which forms fragility function for each damage level of exceedance. Evaluating fragility functions calculated, we observe that T=3.0 spectral acceleration (SA_T3.0) is superior to other IMs, which has lower standard deviation of log-normal CDF and low error of the fit. This indicates that long-period ground motion has more impacts on railway infrastructure system such as tunnel and bridge. It is observed that when SA_T3.0 = 0.1 g, P(DL>1) = 2%, and SA_T3.0 = 0.2 g, P(DL>1) = 23.9%.